530 is the width and stock size on the Busa and large cc bikes. 520 is smaller, lighter weight, and not as strong, and not adviseable to run on the busa.
Gearing is a preference.
Going up teeth on the rear gives you the feel of more bottom to midrange power. Going down on the rear is of course the opposite.
Rough example, stock gen2 busa has 18/43 gearing. It has a restricted top end of 186mph and about 197mph with the restrictions off(this is also what the gearing is capable of, rider, weight, weather, and distance to acheive this all must be factored in). You need to change to 18/42 or 18/41 gearing to pass 200mph. If you continue going down on the rear you will run out of power(stock) to acheive the speed the gearing would allow.
Switching from the stock 190/50/17 rear tire to a 190/55/17 tire(it's taller) would be the equivalent of going down 1 or 2 teeth on the rear.
If you add teeth to the rear and can accelerate quicker, you will still lose mph in every gear.
Unless you want the fastest top speed possible you won't notice the top end lost. A top speed in the mid 170's is possible with a +3 rear.
To front sprockets.
This is where alot of folks get confused.
There is an old assumption that -1 on the front = +3 on the rear. Not true!
Even though the overall gear ratios are similiar on paper, the real world feel is much different.
By going up on the rear you are turning the rear wheel quicker than before, until you run out of rpm(why you lose mph). You have the same available torque from the engine doing this.
If you subtract teeth on the front you are not able to utilize the same amount of torque as effectively.
So the engine is revving higher to accomplish the same as before.
Consider having a 2 gear system to raise a bucket from a well, the principle is the same. The smaller you make the gear on the crank the more times you must turn it to make the second gear go around the same number of times.
Again, you are limited by the engine's rev limit, as it stays the same(unless you raise and build the engine accordingly).
If you've ever ridden a 1000, stock gearing they are a great comparison to a Busa with a -1 front sprocket.
They rev faster and noticebly have less torque.
A busa with a +3 rear will feel as if it has gained torque and raise the front end easier with the same amount of throttle.
A +3 rear also shortens your wheelbase by over an inch(depends on your weight and where your chain slack must be adjusted accordingly).
A shorter wheelbase also makes wheelies easier, as well as the bike's ability to be a little quicker through a turn.
Going up on the rear is great for hard street riding, but not ideal for dragracing a stock wheelbase bike.
I have also changed many gear ratios on alot of dirt and sport bikes over the years. These are my real world experiences. I am not spouting facts I read on gearing commander or any other website.
FYI, if you do use gearing commander, remember that those are numbers of what a gear ratio may be capable of.
How high the engine can rev, where in that range it's making peak power, along with rider and conditions all must be considered.
What would you like to do with your bike? That's the best way to know what gearing would best benefit you.
